In addition to billing customers for an amount of electrical power usage, utilities and other energy providers, bill customers based on the customer peak demand. The cost can be significant, for example, approximately $2.00/kw of total demand per month. Usually the peak rate is held for a period of time, for example, thirteen months or until a higher peak is set, which is then held for thirteen months or other period specified by regulation. The peak demand charge can be significant, as much as several thousand dollars, and is intended to encourage customers to manage their peak demand.
Although not always appreciated, simultaneous HVAC equipment start can be a major contributor to a building's peak demand. Starting currents for electric motors may be six to eight times normally running currents and when the HVAC equipment restarts it may run at full load for a significant period of time as it attempts to recover the environmental conditions in areas it serves. The potentially large number of equipment being started nearly simultaneously, the high starting currents associated with the starts, and the fully loaded condition of the HVAC equipment for a period of time after starting all contribute to a high peak demand. Reducing the peak demand will reduce the peak demand component of electrical energy supply costs. A simultaneous start of HVAC equipment is likely to occur during a recovery from a demand load shedding event. Energy suppliers may have prearrangements with customers during peak electrical demand periods to reduce energy demand by commanding large loads offline or, in the case of HVAC equipment, raising a temperature setpoint in what may be referred to a demand load shedding event. When the need for the lower electrical demand passes, the energy supplier may rescind the demand load shedding event by transmitting a recovery from load shedding command, at which time the customers are free to restart their equipment. If all the equipment was started at the same time, large demand would occur, which could obligate the customer to the higher peak demand charge
Large scale demand management systems require considerable expenditure of funds and are not often deployed in smaller or medium scale properties, for example, a school or hospital campus with numerous buildings, with each building potentially having numerous environmentally controlled zones, each having its own thermostat.
In traditional energy management systems staggered starts are accomplished by a variety of means, typical using knowledge of real time total demand, each system's demand and conditions in each served space. Typically, these systems manage demand based on real-time system wide monitoring and control. These implementations use a full and deep knowledge of the system's components and their state to accomplish precise demand management. This requires a considerable amount of instrumentation, configuration, and expense.
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.